The present invention generally relates to the construction of valves such as are used to control the flow of combustible gas-to-gas-fired appliances and more particularly pertains to improvements in the configuration and construction of such valves in order to reduce the cost of their manufacture.
Regulating authorities typically mandate that valves that are to be used to control the flow of a combustible gas to a gas-fired appliance, such as for example a furnace, water heater or gas-burning fireplace, must be capable of maintaining their integrity when subjected to high temperatures such as may be encountered during a fire so as to preclude the external leakage of gas. This is intended to prevent a fire from being aggravated by the supply of additional fuel leaking from a fire-damaged valve. A side effect of such requirement is that it also typically serves to limit the type of materials that are used in the construction of such valves.
In view of the requirements with respect to fire resistance, valves that are subject to the regulations vis-a-vis high temperature resistance are typically predominantly constructed of metal wherein the melting temperature of such metal exceeds the temperature it is to be exposed to during fire testing. Metal-to-metal contact is relied upon between adjacent components in an assembled valve in order to effect a seal or are adjacent components are sufficiently dimensionally matched such that the failure of any gaskets or seals that may be positioned therebetween would result in minimal, i.e. acceptable, rates of leakage. The failure of gaskets or seals used in the interior of such valves to control the flow of gas through the valve would at worst merely result in the flow of additional gas to the burner where its combustion is adequately provided for and where it would thus not pose an additional hazard during a fire.
The construction of such valves has heretofore called for the manufacture of very tightly dimensioned metal components that require the machining of various cast parts to very close tolerances. Many stopcock configurations employ a conical plug that is rotatably received in a conical cavity formed in a valve body. The plug has an orifice formed in its side that is in fluid communication with an opening formed at its narrow end. The valve body has one duct formed therein that extends from an exterior port to an opening formed in the side of the conical cavity and another that extends from an opening in the base of the conical cavity to a second exterior port. Rotation of the plug so as to align the orifice formed on its side with the opening formed in the side of the conical cavity in the valve body establishes a flow path through the valve. Rotation of the plug so as to avoid any overlap between the orifice formed in the side of the plug and the opening formed in side of the conical cavity serves to positively shut off the flow of gas through the valve.
The interior surface of the conical cavity thus serves as a valve seat for the exterior surface of the plug whereby an effective seal is achieved with the very precise machining of the two surfaces. Machining of the cast metallic components to within 0.001″ is typically followed by a lapping operation to substantially perfectly match the two surfaces. The use of metals and the machining of the various components significantly contribute to the overall cost of such valve. Even minor variations in the machining process contribute to a high rejection rate that further affects the overall cost of manufacture.
A valve is needed that is less expensive to manufacture than heretofore known valves while retaining the ability to control the flow of gas therethrough. More particularly, a valve configuration is needed that obviates the various machining and matching operations that are currently needed to in order to achieve a proper seal. Additionally, a valve configuration is needed that reduces the number of cast metal parts that are needed without compromising the valve's ability to resist external leakage upon being subjected to the elevated temperatures it is subjected to during a fire test.